From 7a82401345ff8229a8e3bf6dd5e0418b7abcaba1 Mon Sep 17 00:00:00 2001
From: Christopher Whelan <topherwhelan@gmail.com>
Date: Mon, 28 Jan 2019 01:19:00 -0800
Subject: [PATCH] PERF: significant speedup in sparse init and ops by using
 numpy in check_integrity

---
 doc/source/whatsnew/v0.25.0.rst |  9 ++++++++-
 pandas/_libs/sparse.pyx         | 15 +++++----------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/doc/source/whatsnew/v0.25.0.rst b/doc/source/whatsnew/v0.25.0.rst
index d0ddb6e09d5555..a9fa8b2174dd04 100644
--- a/doc/source/whatsnew/v0.25.0.rst
+++ b/doc/source/whatsnew/v0.25.0.rst
@@ -23,6 +23,13 @@ Other Enhancements
 -
 -
 
+.. _whatsnew_0250.performance:
+
+Performance Improvements
+~~~~~~~~~~~~~~~~~~~~~~~~
+ - Significant speedup in `SparseArray` initialization that benefits most operations, fixing performance regression introduced in v0.20.0 (:issue:`24985`)
+
+
 
 .. _whatsnew_0250.api_breaking:
 
@@ -187,7 +194,7 @@ Reshaping
 Sparse
 ^^^^^^
 
--
+- Significant speedup in `SparseArray` initialization that benefits most operations, fixing performance regression introduced in v0.20.0 (:issue:`24985`)
 -
 -
 
diff --git a/pandas/_libs/sparse.pyx b/pandas/_libs/sparse.pyx
index f5980998f6db47..5471c8184e458d 100644
--- a/pandas/_libs/sparse.pyx
+++ b/pandas/_libs/sparse.pyx
@@ -72,9 +72,6 @@ cdef class IntIndex(SparseIndex):
         A ValueError is raised if any of these conditions is violated.
         """
 
-        cdef:
-            int32_t index, prev = -1
-
         if self.npoints > self.length:
             msg = ("Too many indices. Expected "
                    "{exp} but found {act}").format(
@@ -86,17 +83,15 @@ cdef class IntIndex(SparseIndex):
         if self.npoints == 0:
             return
 
-        if min(self.indices) < 0:
+        if self.indices.min() < 0:
             raise ValueError("No index can be less than zero")
 
-        if max(self.indices) >= self.length:
+        if self.indices.max() >= self.length:
             raise ValueError("All indices must be less than the length")
 
-        for index in self.indices:
-            if prev != -1 and index <= prev:
-                raise ValueError("Indices must be strictly increasing")
-
-            prev = index
+        monotonic = np.all(self.indices[:-1] < self.indices[1:])
+        if not monotonic:
+            raise ValueError("Indices must be strictly increasing")
 
     def equals(self, other):
         if not isinstance(other, IntIndex):